change mysql 8.0 root password if you forgot it

step1. Stop your databases

service mysqld stop

step2. Modify /etc/my.cnf file add "skip-grant-tables"

vi /etc/my.cnf
[mysqld]
skip-grant-tables
step3. Start mysql

service mysqld start

step4. Select mysql default database

mysql -u root

mysql>use mysql;
step4. Set a new password

mysql> update user set authentication_string=PASSWORD("yourpassword") where User='root';

step5. Remove skip-grant-tables from /etc/my.cnf file.

step6. Restart mysql database

service mysqld restart

mysql -u root -p

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For Ubuntu 19 with MySQL 8.0.17-0ubuntu2, what ended up working for me was a combination of many answers:

In the MySQL's configuration file (/etc/mysql/mysql.conf.d/mysqld.cnf on my machine), under [mysqld], add:

skip-grant-tables = 1
plugin-load-add = auth_socket.so

Restart the MySQL Service;

Connect to MySQL: mysql -uroot;

Run:

UPDATE mysql.user SET authentication_string=null WHERE User='root';
FLUSH PRIVILEGES;

ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY 'pass123';
Stop MySQL and comment skip-grant-tables in the configuration file;

Start MySQL again and this should now work: mysql -u root -ppass123.